1. Field of the Invention
The present invention generally relates to a multilayer substrate and more particularly to a multilayer substrate in which a deformable flexible portion is provided in a multilayer body including a plurality of stacked resin layers and a wiring layer provided in the resin layer.
2. Description of the Related Art
As a conventional multilayer substrate, for example, Japanese Patent Laying-Open No. 2005-311376 discloses a flexible printed circuit board aiming to achieve high reliability even under repeated twisting. The flexible printed circuit board disclosed in Japanese Patent Laying-Open No. 2005-311376 has a bent portion which is straightened out at the time of twisting. The bent portion is formed such that surfaces at opposite edges each have a wave-shape projected-and-recessed pattern extending in a longitudinal direction of a small-thickness board of the flexible printed circuit board.
As disclosed in Japanese Patent Laying-Open No. 2005-311376, a multilayer substrate provided with a flexible (deformable) portion is included in an electric appliance such as a foldable portable telephone. In such a multilayer substrate, with deformation, stress tends to concentrate in a specific portion of the flexible portion, and durability of the flexible portion is compromised. In this case, there is a possibility of breakage of the flexible portion or disconnection of a wiring layer routed in the flexible portion. Such a possibility may also adversely affect electrical characteristics of an electric appliance including the multilayer substrate.